1. Field of the Invention
The invention relates to the field of magnetic disk drives, and more specifically, to patterned magnetic disks (also called “discrete track recording” disks or DTR disks) used in disk drive systems.
2. Related Art
Discrete track recording (DTR) disks or patterned magnetic disks are known in the prior art. See, for example, an article entitled “Beyond discrete tracks: Other aspects of patterned media” by S. E. Lambert, I. L. Sanders, A. M. Patlach, M. T. Krounbi, and S. R. Hetzler, published in Journal of Applied Physics Vol 69(8) pp. 4724–4726. Apr. 15, 1991. Specifically, this article states that the surface of a thin-film disk can be patterned using standard lithographic techniques to form discrete tracks as narrow as 0.5 μm. These studies have been extended to patterns formed when an etched track is broken into discrete segments by etching away some portions of a discrete track. Abrupt changes in magnetization are obtained by DC erasing the medium, giving readback signals with ˜50% of the amplitude of conventional transitions when the gap of the readback head is aligned with the edge of the media pattern.
See also another article entitled “Fabrication and magnetic properties of patterned magnetic recording media” by Tsutomu AOYAMA, Isamu SATO and Shunji ISHIO, published in OYO BUTURI, Vol. 72, No3, p. 0298–0303 (2002). According to this article, discrete track media improve the side writing and side reading phenomena which would be serious problems in conventional continuous magnetic film media at very high track densities. Discrete bit media have a potential of realizing thermally stable magnetic recording beyond 1 Tbit/in2. A fabrication method that involves the use of the combination of nanoimprint and RIE is presented in this article, and magnetic properties of fabricated samples are discussed.
DTR disks should allow manufacturers to pre-format the head position servo information on the disk at the time of disk manufacturing. Also, pre-formatted servoing information may cause a disruption in fly height of a head as it flies over a preformatted area on a DTR disk.
Accordingly, inventors of the current patent application believe that a new servo structure is needed that does not affect the fly height even for the case with a preformatted dedicated servo area.
U.S. Pat. No. 5,739,972 (incorporated by reference herein in its entirety) describes a storage medium in which servo information is recorded in serrated edges of each data track. A thermal component of a MR head's readback signal is extracted and used for servoing. Specifically, as the MR head moves closer towards an outer edge that is serrated at frequency f1, a thermal signal at frequency f1 increases. When the MR head is positioned at the center of a track, the thermal frequency responses from the two serrated edges of the track are near zero. Note that U.S. Pat. No. 5,739,972 requires serrated edges to be present along the entire length of a track, and the track is not apportioned into data sectors v/s servo sectors. Therefore, a readback signal from such a system contains the data signal as well as the servo signal, at all locations along a track.